Projection systems are commonly used in academic, business, and personal environments to project images on screens or walls. The display of these projected images is dependent upon the orientation of the projection systems relative to the screens or walls. For instance, when a projection system is not oriented perpendicularly to a screen, the shape of the image will often appear stretched, deformed, or otherwise misshapen. This distortion of the projected image is often referred to as keystoning, since the shape of distorted image typically resembles a trapezoid or keystone.
There are several ways to correct keystone distortion. Projection systems might, for example, include optics that compensate for keystone distortion. These optics, however, are costly and prone to dust collection that degrades the quality of the projected images. Projection systems might also include gauges used to manually adjust the projected image to eliminate or minimize keystone distortion. These manual adjustments however tend to move the projected image off of the screen or wall and are typically time consuming, cumbersome, and generally an unwelcome set up complication.
Most projection systems additionally include signal processing circuits, for example, to oppositely distort the image to compensate for keystone distortion prior to projecting the image. These signal processing circuits typically distort the image according to distortion values pre-calculated from 100 or more points of the image. Although this technique may alleviate most, if not all, keystone distortion, it is complicated to set-up or recalibrate the projection system. For example, when the projection system is reoriented or repositioned, the system needs to identify new points of the image and recalculate the distortion values, which often requires floating point processes that exceed real time system capability. These complex pre-calculations result in the lack of real time distortion value calculations, which hinder the incorporation of advance functionality into the projection systems, such as image zoom and lens replacement, and impede projection system mobility. Accordingly, a need remains for a system and method for improved keystone correction.